reCAPTCHA Invalid though correct settings - Can not connect to the reCAPTCHA server (0)

[Lily3034]

Since February 2025, reCAPTCHA v3 validation has stopped working on one of my websites, even though it was working perfectly from summer 2023 until February 2025. A client alerted me that they were unable to submit a form. Also note that I have other websites and reCAPTCHA works perfectly on them.

I’ve checked all the usual points:
✅ Correct version used (v3), keys properly placed
✅ Domain correctly added in the reCAPTCHA admin console
✅ Tested with different form plugins (Elementor + Fluent Forms)
✅ Checked for possible conflicts (themes, plugins, updates)
✅ No server-side blocking (curl test OK, no firewall issues)
✅ Created several new keys on 2 different Google accounts → same issue: "Invalid key" or "Can not connect to the reCAPTCHA server (0)"

At this point, I suspect a bug or soft-block on Google's side (maybe triggered by multiple key regenerations?), or possibly a domain-level block.

I’ve deleted all previously generated keys and attempted a clean reconfiguration of reCAPTCHA for the domain, but the issue remains.

When submitting a form (e.g., via the contact page), the following errors appear:
"Can not connect to the reCAPTCHA server (0)"
and also:
"Sorry, your reCAPTCHA is unvalid. Please try again."

This is a serious issue for me, as the forms are essential to my website’s functionality. If the domain is indeed blocked by Google, I have no reliable way to secure submissions or prevent spam.