How were they paired, exactly?
Paired/tethered for call/message forwading?
That is the only way to pair an iPhone/iPad together.
No other ways to do that.
Also, a little hard to help/advise you when you provide NO information about your iPad and iPhone
Here are my questions to you.
Can you, please, confirm what year and model pad and iPhone do you have/own?
The “A” model number can be found on the aluminium back of your iPad in very small print, right under the larger bold print “iPad” on the back of the iPad and in the Settings app, General, About on your iPhone
What iOS/iPadOS version is this iPad and iPhone, currently, running?
What is the rated, internal data storage space/capacity of your iPad and iPhone model and how much of this free, internal data storage capacity is left inside of your iPad model?
All of that additional info can be found in the Settings app, General settings panel, About.
What, exactly, are you trying to do to pair this iPad and iPhone and for what purpose?
No iPad/iPhone combination can directly pair over Bluetooth. THAT has NEVER been possible.
There is ONLY the option to pair/tether an iPad to an iPhone for call and message forwarding.
Please try to attempt to answer all questions asked.
Thank You.