I revisited some Contribution Pages which are working fine in "live" mode. (The credit card transactions are processed and CiviCRM records are updated.) I just discovered that those pages don't work in Test-Drive mode. (Testers receive a 404 error after clicking "Submit", no contribution record is creates, and the Contribution>Payment Processor Administration log shows REJECT1 for the failed transaction.) The text of the 404 error that appears after "Submit" is "Not Found The requested URL was not found on this server. Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request." What's wrong with my test-driving? (CiviCRM 5.48.0 on Wordpress Version 5.9.3)
Additional information. The payment processor is iATS. The credentials for both live payments and test payments are active and unchanged since we launched. I called iATS customer service and they confirm the test credentials are correct.
The URL that generates the 404 error is
I've asked our webmaster to look into other applications that may be interfering with the tests.
More Additional Information:
I notice that occasionally the Contribution Page(s) that I'm trying to test open(s) with this 2-line error message preceding the "Test-drive Your Contribution Page" (screenshot) It doesn't happen every time. Customer Service at iATS explained that that means something is wrong with my set-up and reiterates that the test credentials are valid.
More Additional Information. I found that I can get the Test-Drive functionality to work properly if the transaction amount is $1.00 (no less and no more). I've tried several different Contribution Pages with varying amounts of Fixed and "Other" optional amount. Only $1.00 Test-Drives complete successfully. And to reiterate, all the pages I tested work perfectly in "live" mode, regardless of the amount.