Illegal character in query error

Hi all, I have been pulling data from FRED that was possible through the community’s help in this thread. However, I am facing an error -

ERROR GET Request 3:1 Execute failed: java.lang.IllegalArgumentException: Illegal character in query at index 122: https://api.stlouisfed.org/fred/series/observations?seriesid=M2SL&apikey=xxxxxxxxx&file_type=json

All other data can be pulled without any issue, only this series si causing problems. Any help?