Debugging articles

Everything we have written about debugging.

Debugging FCM INVALID_ARGUMENT, in order of likelihood

The FCM HTTP v1 API returns INVALID_ARGUMENT for about a dozen unrelated mistakes and tells you almost nothing about which one you made. Here is the list, ordered by how often it is actually the cause.

5 August 2026 · 3 min read

Debugging

Expired, invalid, mismatched: three dead push tokens that need three different responses

Most platforms collapse every delivery failure into "failed". Three of the most common failures mean completely different things, and treating them the same is how you either lose real subscribers or keep sending into the void.

1 August 2026 · 3 min read