Can 之间 be equivalent to 之内 in some contexts?
之间 = between (more than one object)

Example:

兩人之间 (between the two persons)

球員之间 (between the players)

教練與球員之间 (Between coach and players)

~

之内 = within (a single object)  

Example:

球队之内 (within the football team) 

组织之内 (within the organization)

公司之內 (within the company)

~

More graphic examples:

两眼之间的距离 (distance between two eyes)

人体之内的器官 (organs within the human body)


  很多的发展过去是在一个行业之间的，我们觉得互联网金融的时代更多机会是在跨业的。


In this context, it should be

很多的发展过去是在一个行业之内的，我们觉得互联网金融的时代更多机会是在跨业的。
(Many developments existed within an industry in the past. We feel that in the era of internet finance, more opportunities are existing between industries)

一个行业 is a single object


过去的发展是在[一个行业之内]的 = the past developments were of [within an industry]
互联网金融的时代的机会是在[行业之间]的 =  internet era's financial opportunities are of [between industries]