Does WordPress support a sub-domain with a different PHP Version

I use a 3-party software package with my site 3DBeliever.com to post my Blog Devotional topics to multiple FaceBook Groups at one time.

That software does not support PHP version 7. Recently, when I received the notification to upgrade to version 7 for WordPress, I upgraded. But, the upgrade broke the other software when I upgraded because it doesn’t support version 7 yet.

They told me to ask if you support a sub-domain having a different version of PHP from the main domain. That is over my head, but I kinda understand it. They support any version of PHP under version 7. Please advise.

My options, I guess, are to:
1. Revert my site back to PHP version 6 or 5 or something so that both are compatible. But is that a bad thing?
2. Create a sub-domain if compatible
3. ????

I could have missed it, but I didn’t see any prior posting about PHP sub-domains having a different version. I would appreciate any insight or help. The vendor offered to set it up for me if it is allowed.
Thanks for your help in advance.