I'd like to submit a proposal, but the "submit" button does not appear on my screen, and the "respond to proposal" button doesn't seem to be active.

The reason the response button wasn’t working is because there is no availability for online submission. It is likely that the issuer has requested only mailed or in-person deliveries. The respond button takes you wherever the issuer has selected to receive responses.

Sometimes it will be natively on the platform, other times it may link you to an email or another URL.