There’s a couple of ways to do that, but I would probably use a StringConcatenator to turn the attribute into WKT, then use a GeometryReplacer...

Agree with @s.jager , there are a couple of ways to do it.  One involves RegEx to get a string in WKT format.  Another involves using AttributeSplitter to build the values into a list and then separate the “Odd” list index values for Longitude values and the “Even” list index values for Latitude to send these to a VertexCreator → LineBuilder

To build out the original great idea though is to need probably some RegEx, as there are two issues  in the raw API string preventing easily building a WKT:

• In the raw string the latitude values (Y) are before the longitude values (X).  These need to be swapped around for WKT as X Y.
• In the raw string, the same delimiter “,” is used between the X Y value-tuple and also between the coordinate pairs.  The X,Y value separator in WKT needs to be a space character instead of “,”  so only these commas, and not the other commas, need to be replaced with a space character.

Now, below this is not the most precise of RegEx expressions to use in StringReplacer (and there are way more capable RegEx people than me on this forum! ), but it should do the job

Sample Data

The core component is then a StringReplacer to transform the string into an inner WKT tuple type format.  These swaps the positions of the Y string value (RegEx Group \1) for the X string value (RegEx Group \2) and puts a space character as the separator.  If there is a “,” after them (RegEx Group \3) then put that back in as well after the X Y value pair.
 

This gives on the Output Eg.
 

From here it is trivial to wrap this inside a WKT LINESTRING(...) and send to a WKT GeometryReplacer
 

Another approach using regular expressions:

1. Replace the FIRST comma with a space. The first comma can be found with the regular expression ^.*?\K,
2. In the resulting string, replace EVERY SECOND comma with a space. Every second comma can be found with the regular expression .*?,.*?\K,
3. Turn the string into WKT
4. Create the geometry from the WKT
5. Flip the object using a CoordinateSwapper

For a more compact workspace, steps 1-3 can be done in one Attributemanager using the string function @ReplaceRegularExpression twice.

thanks a lot for your help.

It works for me with RegularExpressions to create a wkt geometry and afterwards using GeometryReplacer. Sometimes it is difficult to find the correct syntax of the RegEx.