Greys are caused by out-of-sequence submissions. They are solvable by submitting the missing invoices (which may not be possible if one of the invoices in sequence is no longer valid e.g. if deleted). This necessitates keeping a sequential record of submissions which does not necessarily correspond to the invoice sequence within Manager. This is important because users submit “at will” via the relay.
Reds are harder, because it can be one of many things that breaks the rules. The standard way is to validate and reject anything that won’t go through, so the user has the chance to correct it and re-submit.
If the source is open, I am willing to look around and give quick pointers. I can’t commit to working on it though.
Edit: Also, do not resubmit failed invoices. Reading closer, it looks like a specific invoice is the issue. Can you inbox me the submitted invoice data and the link in the output QR code