Reference letter from community association as mandatory criteria

Can I upload a reference letter from a non profit community association that arranges seminars , workshops for local software engineers. I have been invited as a speaker for events.
I have a letter of reference from the president of association. Can it serve in the mandatory criteria. As I have chosen OC1 and OC 3,?
@Savvkin @Francisca_Chiedu

Is this a known organisation? What’s the number of people attending the programme?