Hey I am currently trying to run an IPS unit root test for my study. My 3 main variables involved are GDP, CO2 emissions and GERD. My data set consisted of 50 countries from 1996-2019 (24 years). When I initially ran my IPS unit root tests, it ran and I got output for GDP and CO2 emissions, however, I got an error response which stated "insufficient observations". After reading up on the issue I knew that I either had to drop a few countries or impute my data based on the missing values in my data.

After dropping 5 of the countries from my list, the IPS test ran for my GERD data, however when I tried to run the 1st difference of my GERD, I got an error response saying " Insufficient number of time periods to compute W-t-bar".

Any help to resolve this issue would be much appreciated, also based on the BIC the estimated number of lags were always under 1. So when I conduct my Fisher unit root test, would it be safe to choose the number of lags to be 1?