Can't figure out why I get App Engine flex "Uncaught Error: Call to undefined function Google\Protobuf\Internal\bccomp()"

I'm trying to implement Google's Text-To-Speech API on App Engine flex environment, but get this error:

"PHP message: PHP Fatal error: Uncaught Error: Call to undefined function Google\Protobuf\Internal\bccomp() in /app/web/vendor/google/protobuf/src/Google/Protobuf/Internal/Message.php:941"

Once I solved the problem by requiring BCmath() in my composer.json

{  
    "require": {
        "ext-bcmath": "*",
        "google/cloud-text-to-speech": "^1.0",
        "google/gax": "^1.3",
         "grpc/grpc": "^1.4",
         "google/auth": "^1.8",
         "phpseclib/phpseclib": "^2.0",
         "google/protobuf": "^3.11"        
    }
}

Then after reinstalling /vendor I can't get rid of the error message. I tried to install the BCmath extension by running

sudo apt install php7.2-bcmath

But it says that the extension is already installed. I run also this php -i | grep -i bcmath And get this message

/etc/php/7.2/cli/conf.d/20-bcmath.ini, bcmath BCMath support => enabled bcmath.scale => 0 => 0

The test for bccomp()

php -r "echo bccomp('1', '2');"

I get '-1' as supposed to be. It looks like the function works.

I even tried to enable the BCmath extention in php.ini

extension=bcmath.so

I placed the .ini file in the same directory as my /vendor and index.php. Still, after deployment the app by

gcloud app deploy

I still get the fatal error.

After 5days of breaking head, solution was found. It appears that BCMath is installed in PHP versions >= 7, but NOT enabled on Google App Engine. To enable it I did the following:

1. I have created php.ini file and placed it in the same directory as app.yaml file, which might be different from the root directory of your app (index.php for example).
2. In empty newly created php.ini have added one line:

extension=bcmath

Then require it in composer.json

{
    "require": {

        "ext-bcmath": "*"  
    }
}

Finally deploy the project

 gcloud app deploy

And that's all!