The problem with SBI Maestro card for UPI app linking
For linking a bank account with a UPI enabled app, last six digits of debit card number and expiry date is used. But for State bank of India issued Maestro debit card, there is only "Valid from" date on the card and no expiry date. For this reason many are unable to use SBI maestro card for linking their SBI account with UPI app. Even SBI provided UPI app SBI Pay says it does not support maestro card. This is not true, I was able to link my SBI account with UPI app as described below.
How to Find expiry date of SBI Maestro card
For this internet banking should be enabled for your account. Login to net banking and select e-Services tab on the top. Then from the side menu select "ATM Card Services" and then choose "ATM Card Limit/Channel/Usage Change". Choose your account number and choose continue. You can find the expiry date of your Maestro card as shown in screenshot below.
I was able to use this expiry date to link my SBI account with UPI app. I am not sure if all the SBI Maestro is having the same expiry date as shown above. If you don't have internet banking enabled you can try the above shown date (Jan 2049) for UPI linking.
One problem with SBI Pay app (UPI app provided by SBI) is that it does not support entering expiry date year after 2035, so users are not able to enter 2049 into the app. The solution to this problem is to use any other UPI enabled app that support year greater than 2035 and then link SBI account with UPI. Last 6 digits of debit card and expiry date is required only for initial linking of bank account with UPI and also to set the MPIN that is required for UPI. Once you have linked your SBI app with UPI using any app, you can then use SBI Pay app itself. I used PhonePe app by Flipkart for initial linking. You need not use PhonePe itself, you can use any of the UPI apps listed here or you can use BHIM ,which is an UPI app released by NPCI (National Payment corporation of India)