Discover why the Google Cloud Storage error invalid_grant appears and how we pinpointed every cause after hours of testing and debugging. Our Google Cloud Support Team is always here to help you.
Google Cloud Storage Error invalid_grant Explained
It started with reports from users saying their Google sync and event creation were suddenly failing. After scanning our logs, one message stood out repeatedly: This Google Cloud Storage error invalid_grant 
kept showing up across accounts, old and new. According to the OAuth 2.0 spec (RFC 6749): That meant Google could reject our tokens for several reasons. What followed was a long hunt to uncover the real cause. Here’s every discovery we made.
400 - Google_Auth_Exception
Error refreshing the OAuth2 token, message: ‘{
“error” : “invalid_grant”
}Breaking Down Every Possible Cause
Server Clock and Time Sync Issues
The most common advice was that server time was out of sync. We checked using ntp and confirmed only a 5 ms offset, so no luck there.
Still, for anyone else: a big time offset can cause the Google Cloud Storage error invalid_grant. Remember, ntp resyncs slowly by default, but you can force instant sync if needed.
Checking Offline Access
Next, we verified offline access. Our code already had it:
$client->setAccessType("offline");No issue there either, yet the Google Cloud Storage error invalid_grant persisted.
Considering Google Throttling
Maybe we were being throttled? Our logs said otherwise. Google’s daily event limits weren’t even close to being reached, and raising limits changed nothing.
Expired Refresh Tokens
Google allows up to 25 refresh tokens per account per client. We only generated one token per user and reused it. So, that wasn’t the problem either.
Inactive Accounts
Tokens unused for six months expire, but many of our affected users had joined recently. Another dead end.
Wrong Identifier Used
Using a service account instead of a client ID can cause issues. But since we were dealing with individual user accounts, that didn’t apply to us.
Too Many Access Tokens Too Quickly
At one point, our code requested new access tokens every time instead of checking if the current one had expired.
$client->refreshToken($myRefreshToken);We discovered that this command actually requests a new token every time, not just stores it. After correcting it, we reduced our requests to around 24 per day, which was safe.
PHP SDK Version Issues
We then upgraded our SDK from v1.x.x to v2.0.1 using composer. Still, the Google Cloud Storage error invalid_grant didn’t go away.
Malformed Refresh Tokens
Every refresh token followed the same pattern like this:
1/BtXr3R4lfNdNx6s715Fz0PF2v8wj_aSwDcJTD2a4MWfBactUREfofsF9C7PrpE-jAll valid and consistent. So malformed tokens were ruled out.
Revoked Access
When a user revokes app permissions, Google responds with:
Error refreshing the OAuth2 token, message: ‘{
“error” : “invalid_grant”,
“error_description” : “Token has been revoked.”
}’Interestingly, after 12 hours, Google stops including the “error_description”. After checking, many users who faced this issue didn’t even have our app listed anymore—though they hadn’t manually revoked it.
The Real Cause – Password Resets
Finally, we discovered the real reason. When a user resets or changes their Google password, all their OAuth2 tokens are revoked for security reasons.
That’s why users suddenly saw the Google Cloud Storage error invalid_grant, their passwords had changed, invalidating the token silently.
The fix was simple: users just needed to re-authenticate, and a new refresh token would be issued.
[If needed, Our team is available 24/7 for additional assistance.]
Conclusion
After countless hours of debugging, it turned out the Google Cloud Storage error invalid_grant wasn’t caused by any fancy configuration or code bug. It was plain old password resets revoking tokens.
