You should check the network reply regarding your PSM values.
With at+cpsms the module will send the requested PSM values to the network.
If and which PSM values the network will grant you is reflected in at+cereg URC/output.
Enable URC with: at+cereg=4 or at+cereg=5
Then request at+cereg? output or wait for URC after setting at+cpsms value.
You’ll receive something like:
+CEREG: 4,5,C2F6,031B7B65,9,,,00000001,10101110
CEREG | Active time (T3324): 00000001 | TAU (T3412): 10101110
TAU: 1 minute x 14 = 14 minutes
T3324: 2 seconds x 1 = 2 seconds
Use e.g. calculation tool to decode the output.