Short answer: contact us with what you see. This one is not something to work around, and it is quick for us to identify.
What you might be seeing
You choose the export and nothing appears to happen.
A tab opens, but it is not Cloneable.
The export seems to succeed, but the import page never has your model.
First, rule out the ordinary cause
One version of this is not a fault at all. If the import page asks you to use the extension and you know you have it, that is a different problem with a simple fix: nothing has been sent yet.
If a tab opens and it is not Cloneable
Stop, and tell us the address it opened.
That single detail is what identifies this, and it saves a long back and forth. A screenshot of the tab is ideal, and the address alone is enough.
Do not keep exporting in the hope that it lands somewhere. Repeating it does not help, and the exports do not go where you think.
What not to do
Do not change settings we have not asked you to change. Some of what is on these screens is there for our engineers rather than for customers, and changing it can send your export to an address that is not Cloneable. If you have already experimented, say so when you contact us. It is genuinely useful to know, and nobody is in trouble for it.
What to send us
Where the tab went, or that nothing opened at all
The Katapult address you were working from
Whether the extension said it was connected at the time
Roughly when it started, and whether it ever worked
With those four things we can usually tell you what happened without needing to get on a call.