Aidl Not found error but its installed already?

if the aidl is already installed and you see the error "Aidl not found please install it", you need to check the buildozer.spec file, because this file is telling to buildozer to use aidl in a way Buildozer cannot execute, no matter if the aidl is installed or not, just make sure the following, make sure aidl files are saved into ".buildozer" directory/directories:

/home/yourusername/.buildozer/android/platform/android-ndk-r19b/build-tools/29.0.2/lib64/

The files in that folder must be:

**libbcc.so
libaapt2_jni.so
libbcinfo.so
libclang_android.so
libLLVM_android.so
libc++.so**

or in the directory: /home/yourusername/.buildozer/android/platform/android-ndk-r19b/build-tools/29.0.2/

**dir: lib64
file: mipsel-linux-android-ld
file: mainDexClasses
file: mainDexClassesNoAapt.rules
file: x86_64-linux-android-ld
dir: renderscript
file: bcc_compat
file: zipalign
file: core-lambda-stubs.jar
file: runtime.properties
file: apksigner
file: aidl
file: source.properties
file: dx
file: split-select
file: llvm-rs-cc
file: d8
file: mainDexClasses.rules
file: NOTICE.txt
file: aapt2
file: i686-linux-android-ld
dir: lib
file: aarch64-linux-android-ld
file: dexdump
file: arm-linux-androideabi-ld
file: aapt**

If you have it like that, then, I am using Xubuntu 18.06, now be sure or make sure the spec file indicates exactly the following (remember to edit the buildozer.spec file to make sure you include the relevant info, for example if your project includes md,mp3,atlas,png etc extension make sure you include that in the spec file), anything that is not matching or set up correctly in the buildozer.spec file, will create many different issues when you run buildozer -v android debug, My buildozer.spec file has this inside:

[app]

# (str) Title of your application
title = KivyMD Kitchen Sink

# (str) Package name
package.name = myapp

# (str) Package domain (needed for android/ios packaging)
package.domain = org.test

# (str) Source code where the main.py live
source.dir = .

# (list) Source files to include (let empty to include all the files)
source.include_exts = py,png,jpg,kv,atlas,pyc,ttf,md

# (list) List of inclusions using pattern matching
#source.include_patterns = assets/*,images/*.png

# (list) Source files to exclude (let empty to not exclude anything)
#source.exclude_exts = spec

# (list) List of directory to exclude (let empty to not exclude anything)
#source.exclude_dirs = bin

# (list) List of exclusions using pattern matching
#source.exclude_patterns = buildozer.spec

# (str) Application versioning (method 1)
# version = 0.1
version = 0.1

# (str) Application versioning (method 2)
#version.regex = __version__ = ['\"]([^'\"]*)['\"]
#version.filename = %(source.dir)s/../../kivymd/__init__.py

# (list) Application requirements
# comma seperated e.g. requirements = sqlite3,kivy
#requirements = kivy==master, kivymd, hostpython2
requirements = python3,kivy,kivymd

# (str) The directory in which python-for-android should look for your own build recipes (if any)
#p4a.local_recipes = %(source.dir)s/../../gitlab-ci/p4a-recipes/

# (str) Custom source folders for requirements
# Sets custom source for any requirements with recipes
#requirements.source.kivymd = ../../

# (list) Garden requirements
# garden_requirements =

# (str) Presplash of the application
#presplash.filename = %(source.dir)s/../../kivymd/images/kivymd_logo.png
presplash.filename = /home/jbsidis/Escritorio/aa/kivymd/images/kivymd_logo.png

# (str) Icon of the application
icon.filename = /home/jbsidis/Escritorio/aa/kivymd/images/kivymd_logo.png

# (str) Supported orientation (one of landscape, portrait or all)
orientation = all

# (list) List of service to declare
#services = NAME:ENTRYPOINT_TO_PY,NAME2:ENTRYPOINT2_TO_PY

#
# OSX Specific
#

#
# author = © Copyright Info

#
# Android specific
#

# (bool) Indicate if the application should be fullscreen or not
fullscreen = 1

# (list) Permissions
#android.permissions = INTERNET

# (int) Android API to use
#android.api = 21

# (int) Minimum API required
#android.minapi = 9

# (int) Android SDK version to use
#android.sdk = 20

# (str) Android NDK version to use
#android.ndk = 17c

# (bool) Use --private data storage (True) or --dir public storage (False)
#android.private_storage = True

# (str) Android NDK directory (if empty, it will be automatically downloaded.)
#android.ndk_path =

# (str) Android SDK directory (if empty, it will be automatically downloaded.)
#android.sdk_path =

# (str) ANT directory (if empty, it will be automatically downloaded.)
#android.ant_path =

# (str) python-for-android git clone directory (if empty, it will be automatically cloned from github)
#android.p4a_dir =
#android.p4a_dir = /media/zingballyhoo/Media/Code/Repos/python-for-android

# (str) Filename to the hook for p4a
#p4a.hook =


#p4a.force-build = True


# (list) python-for-android whitelist
#android.p4a_whitelist =

# (bool) If True, then skip trying to update the Android sdk
# This can be useful to avoid excess Internet downloads or save time
# when an update is due and you just want to test/build your package
#android.skip_update = True

# (str) Bootstrap to use for android builds (android_new only)
# android.bootstrap = sdl2

# (str) Android entry point, default is ok for Kivy-based app
#android.entrypoint = org.renpy.android.PythonActivity

# (list) List of Java .jar files to add to the libs so that pyjnius can access
# their classes. Don't add jars that you do not need, since extra jars can slow
# down the build process. Allows wildcards matching, for example:
# OUYA-ODK/libs/*.jar
#android.add_jars = foo.jar,bar.jar,path/to/more/*.jar

# (list) List of Java files to add to the android project (can be java or a
# directory containing the files)
#android.add_src =

# (str) python-for-android branch to use, if not master, useful to try
# not yet merged features.
#android.branch = master

# (str) OUYA Console category. Should be one of GAME or APP
# If you leave this blank, OUYA support will not be enabled
#android.ouya.category = GAME

# (str) Filename of OUYA Console icon. It must be a 732x412 png image.
#android.ouya.icon.filename = %(source.dir)s/data/ouya_icon.png

# (str) XML file to include as an intent filters in <activity> tag
#android.manifest.intent_filters =

# (list) Android additionnal libraries to copy into libs/armeabi
#android.add_libs_armeabi = libs/android/*.so
#android.add_libs_armeabi_v7a = libs/android-v7/*.so
#android.add_libs_x86 = libs/android-x86/*.so
#android.add_libs_mips = libs/android-mips/*.so

# (bool) Indicate whether the screen should stay on
# Don't forget to add the WAKE_LOCK permission if you set this to True
#android.wakelock = False

# (list) Android application meta-data to set (key=value format)
#android.meta_data =

# (list) Android library project to add (will be added in the
# project.properties automatically.)
#android.library_references =

# (str) Android logcat filters to use
#android.logcat_filters = *:S python:D

# (bool) Copy library instead of making a libpymodules.so
#android.copy_libs = 1

# (str) The Android arch to build for, choices: armeabi-v7a, arm64-v8a, x86
#android.arch = armeabi
android.arch = armeabi-v7a

#
# iOS specific
#

# (str) Path to a custom kivy-ios folder
#ios.kivy_ios_dir = ../kivy-ios

# (str) Name of the certificate to use for signing the debug version
# Get a list of available identities: buildozer ios list_identities
#ios.codesign.debug = "iPhone Developer: <lastname> <firstname> (<hexstring>)"

# (str) Name of the certificate to use for signing the release version
#ios.codesign.release = %(ios.codesign.debug)s


[buildozer]

# (int) Log level (0 = error only, 1 = info, 2 = debug (with command output))
log_level = 2

# (int) Display warning if buildozer is run as root (0 = False, 1 = True)
warn_on_root = 1

# (str) Path to build artifact storage, absolute or relative to spec file
# build_dir = ./.buildozer

# (str) Path to build output (i.e. .apk, .ipa) storage
# bin_dir = ./bin

#    -----------------------------------------------------------------------------
#    List as sections
#
#    You can define all the "list" as [section:key].
#    Each line will be considered as a option to the list.
#    Let's take [app] / source.exclude_patterns.
#    Instead of doing:
#
#[app]
#source.exclude_patterns = license,data/audio/*.wav,data/images/original/*
#
#    This can be translated into:
#
#[app:source.exclude_patterns]
#license
#data/audio/*.wav
#data/images/original/*
#


#    -----------------------------------------------------------------------------
#    Profiles
#
#    You can extend section / key with a profile
#    For example, you want to deploy a demo version of your application without
#    HD content. You could first change the title to add "(demo)" in the name
#    and extend the excluded directories to remove the HD content.
#
#[app@demo]
#title = My Application (demo)
#
#[app:source.exclude_patterns@demo]
#images/hd/*
#
#    Then, invoke the command line with the "demo" profile:
#
#buildozer --profile demo android debug

the aidl package I downloaded from https://dl.google.com/android/repository/build-tools_r29.0.2-linux.zip My buildozer.spec files contains directories indicating my username jbsidis, remember to change/replace that with your own username.

For this problem solution very very simple just use the Folder which you used the first time.

Note: This solution work when you already converted code file into apk file successfully use that folder for debugging. Copy your .py and .kv files in this folder

I am working on an android app when I was trying to convert code file into APK(using the command "buildozer android debug") I was also facing the same kind of problem(Aidl not found, please install it) but aidl already installed.