Problem installing, too many redirections

[stormriderstudios]

I'm trying to install SMF for the first time, I've setup the database, I've uploaded the files and set the file permissions but when I go to the install.php url it constantly redirects before erroring out.

SMF version: 2.0.17
PHP version: 7.3.24 (also tried 7.0.33 and 5.6.40)

I'm installing on a subdomain, I've tried multiple subdomain names all fail.
I've tried it on another domain which works, and on a subdomain of that other domain, which also works.

I'm lost - what could cause this?

[Looking]

The issue MIGHT be that the path is not correct, it all depends on how the subdomain was set up as different server control software does things differently (Direct Admin vs Cpanel for an example).

What are the error messages saying?

[stormriderstudios]

There's nothing in the server log files.
The subdomain was created using plesk and the only difference is that the domain name is hosted externally, but has a * A record pointing to my server.

Firefox just shows:

"The page isn't redirecting properly

An error occurred during a connection to hxxp:subdomain.domain.name [nonactive]. (removed for security)

    This problem can sometimes be caused by disabling or refusing to accept cookies."

Firefox web tools just shows the page reloading install.php over and over until it fails

[Looking]

Was this recently setup and not properly propagated yet? That error message usually points to something not right long before install.

[stormriderstudios]

The domain has been in place for several months. The subdomain is brand new but I didn't think that would matter.
I've also messaged the server company to get them to look into it.

Any other checks I can do other than a dns lookup (which comes back with the correct IP address)?

There's no chance the htaccess file on the main domain would affect the subdomain right? Possibly a daft question whichever way the answer goes...

[Sir Osis of Liver]

Is the subdomain in or above /public_html?

[stormriderstudios]

It's httpdocs on plesk but it's above (or rather alongside) - not within

[Sir Osis of Liver]

Can you reach anything in subdomain?  If SMF files are there, you should be able to link directly to agreement.txt.

[stormriderstudios]

Problem solved!
Looks like the htaccess file from the main domain had been copied into the subscriber root directory - just above httpdocs and the subdomain directory.

thanks for all your help and sorry for being a doofus!