You’ll have to apply for the LTA DataMall API access from the link below. It takes only 5 mins. You then paste the key in the text box below

https://www.mytransport.sg/content/mytransport/home/dataMall/request-for-api.html

You then need to provide the bus-stop number and the buses you want. See further down. An entry named Office has been provided as an example.