Complex sentence: His demand was rejected, since the post was promised to Ghaziuddin Khan, but Farrukhsiyar offered him a post as regent under the name of "wakil-e-mutlaq".
Split into simpler sentences: His demand was rejected as the post was promised to Ghaziuddin Khan. However Farrukhsiyar offered him a post of regent under the name of "wakil-e-mutlaq".