Attach carport with ground anchors - how to align?

So in the assembly instructions only H-anchors and concrete foundations are mentioned. How the post is to be attached in the H-anchor is not stated.

Then why don't you take the H anchor? Then two bolts are required.

Too complicated with embedding in concrete

So, the ground anchors are set, also somewhat vertically aligned;-) That was pretty difficult because there were all kinds of roots and stones in the ground. Now the question is, how do you get all the anchors to the same height? Simply stretch a string and check with a line level or is there another trick?

place a straight beam on it (at least over two, preferably over several, also across) and place a spirit level on it, then you roughly have the same heights. It becomes precise when you build the carport and align the cross and longitudinal beams on top with a spirit level

Unfortunately, I do not have a beam that long and straight. What do you think about the string and level method? Is that possible?