From the /questions doc:

...use the tagged parameter with a semi-colon delimited list of tags. This is an and contraint(sic), passing tagged=c;java will return only those questions with both tags...

^{(Emphasis added)}

If you want questions that have either tag, use the /search route (or /search/advanced).

For example:
/2.2/search?tagged=google-docs-api;firebase-database;android-sdk;google-drive-sdk...

As for why the API sometimes differs from the website search, that has been asked a few times both here and elsewhere. EG, see Why is there a difference between "questions" and "search" in API?.

From the /questions doc:

...use the tagged parameter with a semi-colon delimited list of tags. This is an and contraint(sic), passing tagged=c;java will return only those questions with both tags...

^{(Emphasis added)}

If you want questions that have either tag, use the /search route (or /search/advanced).

For example:
/2.2/search?tagged=google-docs-api;firebase-database;android-sdk;google-drive-sdk...

As for why the API sometimes differs from the website search, that has been asked a few times both here and elsewhere. EG, see Why is there a difference between "questions" and "search" in API?.

But a common reason for API calls that use dates (fromdate etc.) to return unexpected results is not taking into account how the API handles unix epoch time.

From the /questions doc:

...use the tagged parameter with a semi-colon delimited list of tags. This is an and contraint(sic), passing tagged=c;java will return only those questions with both tags...

^{(Emphasis added)}

If you want questions that have either tag, use the /search route (or /search/advanced).

As for why the API sometimes differs from the website search, that has been asked a few times both here and elsewhere. For example, see Why is there a difference between "questions" and "search" in API?.

From the /questions doc:

...use the tagged parameter with a semi-colon delimited list of tags. This is an and contraint(sic), passing tagged=c;java will return only those questions with both tags...

^{(Emphasis added)}

If you want questions that have either tag, use the /search route (or /search/advanced).

For example:
/2.2/search?tagged=google-docs-api;firebase-database;android-sdk;google-drive-sdk...

As for why the API sometimes differs from the website search, that has been asked a few times both here and elsewhere. EG, see Why is there a difference between "questions" and "search" in API?.