l was planning to travel to Beijing then .
这个句子确实找不出错误之处.
因为,搭配都有案可稽.
plan to do sth:计划做某事；计划去做
was planning to...then:当时正计划去做.,词形变化也都无差错.
travel to:vt.去…（旅行）
Today we travel to Paris,France,to visit one of the most famous and most visited art collections in the world.
可见,这句话完全正确!