Basically, the French and the British did not allow the Czechs to have a representative at the Munich Conference because they were afraid that the Czechs would ruin the deal that they wanted to make with Hitler. The French and the British had no desire to fight for Czechoslovakia. They wanted to make a deal in which they would give the country to Hitler rather than fighting.
If that was their goal, there was no way they wanted the Czechs at the conference. The Czech government would never have agreed to be given to Germany. They would have raised a fuss and maybe caused the whole deal to fall through. France and England did not want that at all.
So the French and the English excluded the Czechs because they did not want the Czechs to ruin the deal they were going to make.
The Czech president, Benes, was prepared for war in case Germany launched an offensive. He had already taken steps to secure military support by approaching the USSR, France and Britain. These nations agreed to support Czechoslovakia in the event that Germany declared war against it. In fact, the USSR guaranteed Czechoslovakia the support with the others nation’s support being dependent on the others’. It is no wonder that the Soviet Union was not invited to the Munich conference as well. Even though these nations had pledged to offer military support to Czechoslovakia, none of them wanted war. Britain and France felt ill prepared for combat and felt somewhat threatened by Germany’s military might. Knowing that Czechoslovakia was determined to secure its sovereignty by any means necessary, and was prepared for war, it became apparent that it would be left out during the Munich discussions. It would be easier to settle the matter by yielding to Hitler’s demands and coercing Czechoslovakia to submit instead of resorting to military violence.
The Munich conference included France, GB, Germany and Italy. France and GB were afraid of Hitler and said they wouldn't protect Czech and in 1939 Czech was invaded by Hitler. The others countries did not want to risk the deal they had planned if Czech came.