Yhyjyk

What is wrong with this table please? Probably $sidegree$. Thank you

documentclass[a4paper]article
usepackageamsmath, amsthm, amssymb, mathtools
usepackagesiunitx
begindocument
begintable[h!!]
small
renewcommandarraystretch1.2

setlengthtabcolsep3pt
begintabular*linewidthl@extracolsepfillc c cS[table-format=3.1]c

De &V (km) &S ($sidegree$) &P (min) &Per (dny)\
hline
A & 840 & 98,7& 101,5& 0,07048\
B & 785 & 98,7& 101,4& 0,07041\
C & 775-790& 98,6& 100,4& 0,06972\
D & 612-640& 98,0& 97,1& 0,06743\

endtabular*
endtable
enddocument

You are making the last column of your table as a SI (S) column, so you must wrap non-number contents in that column inside braces. Btw h!! is nonsense.

documentclass[a4paper]article
usepackageamsmath, amsthm, amssymb, mathtools
usepackagesiunitx
begindocument
begintable[h!]
small
renewcommandarraystretch1.2

setlengthtabcolsep3pt
begintabular*linewidthl@extracolsepfillc c c S[table-format=3.1]c
De & V (km) & S (sidegree) & P (min) &Per (dny)\
hline
A & 840 & 98,7 & 101.5 & 0,07048\
B & 785 & 98,7 & 101.4 & 0,07041\
C & 775-790 & 98,6 & 100.4 & 0,06972\
D & 612-640 & 98,0 & 97.1 & 0,06743
endtabular*
endtable
enddocument

However it will change the commas to dots in the last column. To avoid this, read this question.

It seems to me that you are trying to make the second last column to be a SI column, so you should place S[table-format=3.1] somewhere else. My final answer:

documentclass[a4paper]article
usepackageamsmath, amsthm, amssymb, mathtools
usepackage[locale=FR]siunitx
begindocument
begintable[h!]
small
renewcommandarraystretch1.2
setlengthtabcolsep3pt
begintabular*linewidthl@extracolsepfillc c S[table-format=3.1]c c
De & V (km) & S (sidegree) & P (min) & Per (dny)\
hline
A & 840 & 98,7 & 101,5 & 0,07048\
B & 785 & 98,7 & 101,4 & 0,07041\
C & 775-790 & 98,6 & 100,4 & 0,06972\
D & 612-640 & 98,0 & 97,1 & 0,06743
endtabular*
endtable
enddocument

However, take care of the last column. I intentionally keep it, but you may want to reduce its size.

i would wrote your table narrower:

and for last three columns use S column type:

documentclass[a4paper]article
usepackageamsthm, amssymb, mathtools% mathtools load `amsmath
usepackage[locale=FR]siunitx

begindocument
 begintable[h!]
renewcommandarraystretch1.1
begintabularl c
 S[table-format=2.1]
 S[table-format=3.1]
 S[table-format=1.5]
De & V (km) & S (sidegree) & P (min) & Per (dny)\
 hline
A & 840 & 98,7 & 101,5 & 0,07048\
B & 785 & 98,7 & 101,4 & 0,07041\
C & 775-790 & 98,6 & 100,4 & 0,06972\
D & 612-640 & 98,0 & 97,1 & 0,06743
endtabular
 endtable
enddocument

note curly braces around column headers in S columns!