Can i put an iPhone SIM card in an iPad

A Carrier SIM card from a Mobile Phone will generally not work with a Cellular iPad.

An WiFi & Cellular model of iPad requires a Data SIM (whilst often being the same size, it functionally different) - or for compatible models, the embedded AppleSIM or eSIM may be utilised.

Set up mobile data service on your Wi-Fi + Cellular model iPad – Apple Support

The following devices support the same SIM card size:

• iPad (7th generation)
• iPad (6th generation)
• iPad (5th generation)
• iPad Pro
• iPad Air and later
• iPad mini and later

Make sure to check with your carrier that you can use iPad with your iPhone SIM card, as it may be registered for use only on your iPhone.

Did you buy an iPad that is WiFi and Cellular? If it is WiFi only, then no, you cannot.