Work through these in order.
Check the address. Copy it from your brand's connect page rather than typing it. Each brand has its own.
Check the tool's plan. Several tools only allow a custom connection on their paid tiers, and a few only on enterprise plans.
Check the approval finished. Connecting opens a browser window; if you closed it before approving, the tool has no permission and will usually say nothing useful about why.
Check the workspace is not paused. A paused workspace refuses connections and says so, but the message appears inside your AI tool rather than in Setu.
If none of that is it, write to us with the tool name and what it said. A connection that should work and does not is a bug we want.
Still stuck? hello@devalok.in, and a person will reply.