Creating events using REST APIs is not working for custom events with varbinds greater than 9.
CA has created Program Temporary Fix (PTF) to resolve this issue:
10.2.3 (GA) - Spectrum_10.02.03.PTF_10.2.339 patch
10.2.3 + Spectrum_10.02.03.BMP_10.2.301 - Spectrum_10.02.03.PTF_10.2.340 patch
Please open a case with CA Support to obtain the PTF patch fix that you need for the version of CA Spectrum you are running.