Code Injection - requires an Upgrade

I am new to SquareSpace.  We have a personal version as it is for a small non-profit.  I bought a PlugIn and it worked okay on my test site (which is a copy of my production site).  When I tried to add the Injection code to Production site, it said "Upgrade required".   I have not gotten an answer yet from the company - SquareSpace.  this seems odd.  Thanks for your feedback.

@SkipperNev Yes, code injection is a premium feature; it requires a business plan.

Thank you.

What plugin do you use? With some plugin code, you can still insert the appropriate area for it to work with Personal Plan (your current plan)