UK Visitor Visa Rejected

Hi all.
Was rejected a visit visa for less than 6 months.
The reason was:
"you state that you r a business partner at company xxxx ,however from your application and supporting documents i was unable to establish how you are connected to this business".

We are business partners myself and my sister. The company is registered under my sis.She began the the business by her own and later on i joined her.We did not see the need of changing to both our names.I contributed to some capital back in 2014 and i was added as the signatory on the business a/c at the bank.

Wat other evidence should i provide?.
I had provided a letter from my sis confirming that im a business partner and the amount i will be spending for the business towards the trip
An affidavit from the lawyers that im a business partner and the date i joined.