This is indeed Bamanda (that is the correct name of the state) 1890 ĽA (SG 10c/Benns BM10b/Preston 9h) on thin reddish purple paper, from position R4/4(16) in Benns Setting Va.
Unfortunately Gibbons clubs SG 10b and 10c in the same setting V and Benns included SG 10c as a transient state of sub-setting Va when SG 10c should have been attributed to a separate sub-setting than Benns sub-setting Va.
Gibbons is just for beginners as far as Bamanda 1st and 2nd issues are concerned. For details I would suggest to go thru Benns' handbook.Bamra Its Postage Stamps, Postmarks, Postal Stationery, Fogeries and Fiscals
Raymond John Benns.
The India Study Circle for Philately, Eastleigh, England 1982